REVIEW 4 major objections 6 minor 20 references
Performance of the image persistence model for Euclid infrared detectors
T0 review · 4 major / 6 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read A fluence-dependent power-law model predicts image persistence in Euclid's NISP infrared detectors to within a few electrons, and in-flight data are on average compatible with ground calibration.
desk verdict Solid H2RG persistence data and a genuinely new above-saturation effect, but the few-electron accuracy claim is in-sample and flight agreement stays qualitative. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the power-law persistence law with fluence-dependent parameters. The form $I(S,t)=\alpha(S)(\tau/(t-t_0+\tau))^{\beta(S)}$ encodes a broad distribution of trapping time constants, and the two empirical functions $\alpha(S)$ and $\beta(S)$ capture how the initial current and the decay slope respond to stimulus strength. The fitting procedure is two-stage: for each fluence level, $\alpha$ and $\beta$ are estimated from the integrated persistence current in dark ramps, and then the six constants $a_1,b_1,c_1,a_2,b_2,c_2$ are fitted pixel by pixel to describe the fluence dependence. The parameter $\tau$ prevents divergence at the end of exposure, and using per-pixel parameters lets the model absorb the nonuniform trap distributions seen in the persistence maps.
What would settle it
Take an in-flight sequence in which a bright star has crossed a NISP detector, run the six-parameter model forward from the actual fluence history, and compare the predicted persistence with the measured residual image in the next pointing; if the residual exceeds a few electrons r.m.s. for one of the detectors flagged as discrepant, the ground-to-flight transfer claim fails.
Extended reading notes
Core claim
The central claim is that persistence current in NISP's HgCdTe H2RG detectors below saturation follows the power-law decay $$I(S,t)=\$\alpha$(S)\left(\frac{\tau}{t-t_0+\tau}\right)^{\$\beta$(S)},$$ with the fluence-dependent amplitude and index $$\$\alpha$(S)=(a_1+b_1S)\left(1-\exp(-S/c_1)\right),\qquad \$\beta$(S)=a_2\left(1+S/b_2\right)^{c_2}.$$ Fitting these six parameters per pixel in two stages --- first per-fluence $\alpha,\beta$ from the integrated current in up-the-ramp dark exposures, then their stimulus dependence --- yields a model whose predicted persistence ramps have a bias of roughly 5--10% of the persistence signal (a few electrons) and per-pixel noise below 8 e r.m.s. for all stimuli tested. The paper further reports that persistence amplitudes across the focal plane are typically about 1% of the stimulus below saturation, that a power law fits the decay better than one, two, or three exponentials, and that in-flight persistence parameters are on average compatible with ground values with the same qualitative trends.
Load-bearing premise
The few-electron accuracy in flight depends on the assumption that persistence parameters measured on the ground at 85 K with flat-field stimuli transfer to the real Euclid observation sequence; the paper reports flight parameters are only on average compatible with ground values and can differ significantly for some detectors, without a quantitative threshold.
Editorial extensions
If this is right
- If the model is correct, Euclid's processing pipeline can predict persistence from the recent exposure history and either mask or subtract afterimages in ordinary survey frames.
- A few-electron predictive accuracy would remove a known systematic in photometry and redshift measurements, directly protecting the weak-lensing and galaxy-clustering analyses.
- Because $\beta$ rises with fluence, persistence decays faster after brighter stimuli, so any correction must weight past exposures by their own signal levels rather than by a single fixed decay curve.
- The stabilization measurements imply that calibration sequences taken after the detector has been dark for a long time reach steady state only after about 30 minutes, so persistence parameters should be derived from steady-state exposures.
- Saturating stimuli change the persistence pattern and leave a long-lived altered detector state, so the below-saturation model does not apply after saturation and saturating events need separate handling.
Reading between the lines
- The same two-stage fitting scheme could be applied to any H2RG-based instrument with a flat-field stimulus sequence; the functional forms are generic and not tied to Euclid's specific filters or readout scheme.
- The paper's 'on average compatible' statement is not backed by a statistical test; a concrete per-detector acceptance threshold, defined before comparing ground and flight parameters, would turn this into a falsifiable transfer check.
- The measured dip in detected stimulus after a long dark period is not captured by the model, suggesting a natural extension in which an additional state variable tracks how many traps are filled at the start of each exposure.
- A direct end-to-end test would be to feed the model the actual fluence history of a real Euclid pointing sequence containing bright stars and compare predicted persistence maps against the next dark or science exposure, quantifying the useful correction power in routine operations.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents an empirical image-persistence model for the 16 H2RG detectors of the Euclid NISP instrument. Ground characterisation data at 85 K with flat-field stimuli between 5,000 and 95,000 e are used to fit a power-law decay current I(S,t)=alpha(S)(tau/(t-t0+tau))^beta(S), with fluence-dependent coefficients alpha(S)=(a1+b1*S)(1-exp(-S/c1)) and beta(S)=a2*(1+S/b2)^c2, giving six parameters per pixel. The model is used to predict persistence ramps in MACC mode; the bias and noise are estimated from residuals over 15 repeated sequences, and flight Performance Verification data are compared with ground results. The paper also reports persistence above saturation, a pattern inversion at saturation, and a long-term change of detector state after saturating stimuli.
Significance. The model is directly relevant for Euclid operations: persistence correction or masking is needed for weak-lensing and photometric measurements, and the paper documents per-detector and per-pixel variability for all 16 flight detectors. The main strengths are the large ground dataset, the per-pixel approach, and the explicit attempt to compare with in-flight PV data. However, as it stands the central accuracy claim is supported only by in-sample residuals, and the flight comparison is qualitative, so the paper's operational conclusion requires additional quantitative validation.
major comments (4)
- [§2.5, Eq. (2)] The statement that a power law fits better than an exponential or a sum of two or three exponentials is not supported by any reported fit statistics. Please provide a quantitative model comparison (e.g., chi-square per degree of freedom, AIC/BIC, or residual r.m.s. per candidate model) for a representative set of pixels and fluences; without this, the choice of Eq. (2) is not established.
- [§2.6] The quoted accuracy ("bias ranges from about 5% to 10%", "median noise lower than 8e r.m.s.") is computed from residuals against the same 15 sequences used to fit alpha_i and beta_i in §2.5. This is an in-sample validation. An out-of-sample test (e.g., leave-one-sequence-out, or fit on a subset of fluences and predict the remaining ones) is needed before the Summary's "accuracy of a few electrons" can be accepted.
- [§2.7 and §5] The flight verification is only qualitative. The text says flight-derived alpha and beta are "on average compatible" with ground values but that differences "can be significant for some detectors", and no statistical test, per-detector values, or uncertainties are given. Because flight data are integrated over 87 s and 550 s MACC modes, the short-term decay parameters are not independently constrained in flight. Please quantify the ground-to-flight comparison per detector and state explicitly what the flight data can and cannot constrain.
- [§2.5, Eq. (2)] The parameter tau is introduced to avoid divergence at t=t0 but its treatment is not specified: it is not stated whether tau is fixed a priori, fitted per pixel, per fluence, or per detector. If fitted, tau is degenerate with alpha and beta; if fixed, its value and justification should be stated. The same applies to the definition of t0.
minor comments (6)
- [Title and header] The title contains a missing space: "forEuclid" should read "for Euclid".
- [§2.1] The notations UTR(286) and UTR(76) are used without definition; please define the readout mode before first use.
- [§2.6 footnote] The MACC(ng,nf,nd) notation is defined in the footnote but used in the main text; please ensure the definition is given at first use in the text.
- [§2.8] The sentence "indicates the the time constants of capture" contains a duplicated article; also, "in agreement with suggestions of [19] while [11] proposes" is a run-on sentence that should be rephrased.
- [§5] The sentence "The signal-dependent persistence model derived in this work for stimuli below saturation that describes persistence signals with the accuracy of a few electrons" lacks a main verb and should be rephrased.
- [Figure 7 caption] The caption contains a typo: "bout 5000" should read "about 5000".
Circularity Check
Reported few-electron accuracy is an in-sample residual: §2.6 validates the model on the same 15 sequences used to fit its six per-pixel parameters, and §2.7's flight check is only qualitative.
-
fitted input called prediction
[Section 2.6, compared with Section 5 Summary; fit described in Section 2.5]
"The accuracy (bias) of the signal-dependent model was calculated per pixel as the average (over 15 sequences for the same fluence) difference between the linear slope fitted on the model ramp in MACC(ng,nf,nd)† generated using Eqs. (2), (3) and (4) and the linear slope fitted on the data in the same MACC mode."
The six per-pixel parameters (a1, b1, c1, a2, b2, c2) are fitted to exactly these ground 15-sequence data in Section 2.5: 'first, we fit αi and βi per fluence Si on exposures up the ramp, and then we fit the dependence of α and β on the stimulus amplitude S for all pixels independently.' The 'accuracy of a few electrons' asserted in the Summary is therefore the residual of the model against its own fitting data, not an independent prediction. The only external check, Section 2.7, is qualitative ('on average compatible', differences 'can be significant for some detectors') and cannot confirm few-electron accuracy for short-term decay because flight data are integrated over 87 or 550 s. Thus the headline accuracy claim reduces to an in-sample goodness-of-fit.
full rationale
The paper is an empirical modelling paper: the persistence model's six parameters per pixel are obtained by fitting ground characterization data in Section 2.5. The central accuracy claim in Section 5 ('describes persistence signals with the accuracy of a few electrons') is supported by Section 2.6, which measures the difference between model-generated MACC ramps and slopes fitted to the same 15 sequences at the same fluences used for the fit. That is an in-sample residual, so the reported accuracy is not an out-of-sample prediction. The flight comparison in Section 2.7 is genuinely external evidence, but it is only qualitative and explicitly notes that ground-to-flight differences 'can be significant for some detectors'; it also states that flight data, integrated over 87 or 550 s, reduce precision for short-term persistence decay. Consequently the few-electron predictive accuracy in flight is not established by independent data. No load-bearing self-citation or uniqueness-imported-from-authors pattern is present: the cited prior Euclid detector papers are instrument-characterization references, and the power-law ansatz is compared against data rather than smuggled in via citation. Because the central quantitative accuracy claim reduces to the fit residual while a partial external check exists, the circularity score is 6 rather than higher.
Assumptions & free parameters
free parameters (8)
- a1 (per-pixel, in alpha(S)) =
Not tabulated in text
- b1 (per-pixel, in alpha(S)) =
Not tabulated
- c1 (per-pixel, in alpha(S)) =
Not tabulated
- a2 (per-pixel, in beta(S)) =
Not tabulated
- b2 (per-pixel, in beta(S)) =
Not tabulated
- c2 (per-pixel, in beta(S)) =
Not tabulated
- tau (in Eq. 2) =
Not specified
- alpha_i and beta_i per fluence (intermediate) =
Not tabulated
assumptions (5)
- domain assumption Power-law decay is the correct functional form for persistence current below saturation.
- domain assumption Persistence from successive exposures superposes linearly.
- domain assumption The trapping and release model of Smith et al. [17,18] is the correct physical picture.
- domain assumption Dark exposures after a flat-field contain only persistence signal, with no other time-dependent systematics.
- domain assumption Detectors reach a steady-state of capture and release after about 30 minutes in the dark.
Cite this review
Pith. "Pith review of Performance of the image persistence model for Euclid infrared detectors." pith.science (2026). https://pith.science/paper/OWUDXZHA
@misc{pith2026250602775,
author = {Pith},
title = {Pith review of: Performance of the image persistence model for Euclid infrared detectors},
year = {2026},
howpublished = {\url{https://pith.science/paper/OWUDXZHA}},
note = {Machine review of arXiv:2506.02775}
}
read the original abstract
Large-format infrared detectors are at the heart of major ground and space-based astronomical instruments, and the HgCdTe HxRG is the most widely used. The Near Infrared Spectrometer and Photometer (NISP) of the ESA's Euclid mission launched in July 2023 hosts 16 H2RG detectors in the focal plane. Their performance relies heavily on the effect of image persistence, which results in residual images that can remain in the detector for a long time contaminating any subsequent observations. Deriving a precise model of image persistence is challenging due to the sensitivity of this effect to observation history going back hours or even days. Nevertheless, persistence removal is a critical part of image processing because it limits the accuracy of the derived cosmological parameters. We will present the empirical model of image persistence derived from ground characterization data, adapted to the Euclid observation sequence and compared with the data obtained during the in-orbit calibrations of the satellite.
Figures
Figures from the paper (7 more)
Reference graph
Works this paper leans on
-
[1]
Understanding Persistence: A 3D Trap Map of an H2RG Imaging Sensor
Rachel E. Anderson, Michael Regan, Jeff Valenti, and Eddie Bergeron. Understanding persistence: A 3d trap map of an h2rg imaging sensor. arXiv e-prints, art. arXiv:1402.4181, 2014
work page Pith review arXiv 2014
-
[2]
R. Barbier, C. Buton, J. C. Clemens, L. Conversi, A. Ealet, S. Ferriol, F. Fornari, W. Gillard, R. Kohley, B. Kubik, C. Rosset, A. Secroun, B. Serra, G. Smadja, and J. Zoubian. Detector chain calibration strategy for the Euclid flight IR H2RGs. In Andrew D. Holland and James Beletic, editors, High Energy, Optical, and Infrared Detectors for Astronomy VIII...
-
[3]
Carlotta Bonoli, Andrea Balestra, Favio Bortoletto, Maurizio D’Alessandro, Ruben Farinelli, Eduardo Med- inaceli, John Stephen, Enrico Borsato, Stefano Dusini, Fulvio Laudisio, Chiara Sirignano, Sandro Ventura, Natalia Auricchio, Leonardo Corcione, Enrico Franceschi, Sebastiano Ligori, Gianluca Morgante, Laura Patrizii, Gabriele Sirri, Massimo Trifoglio, ...
work page 2016
-
[4]
Euclid Collaboration: Cropper, M. et al. Euclid. II. The VIS Instrument. arXiv e-prints , art. arXiv:2405.13492, May 2024. doi: 10.48550/arXiv.2405.13492
-
[5]
Euclid Collaboration: Jahnke, K. et al. Euclid. III. The NISP Instrument. arXiv e-prints, art. arXiv:2405.13493, May 2024. doi: 10.48550/arXiv.2405.13493
-
[6]
Euclid Collaboration: Mellier, Y. et al. Euclid. I. Overview of the Euclid mission. arXiv e-prints, art. arXiv:2405.13491, May 2024. doi: 10.48550/arXiv.2405.13491
-
[7]
Euclid Collaboration: Schirmer, K
M. Euclid Collaboration: Schirmer, K. Jahnke, and Seidel, G., et al. Euclid preparation. XVIII. The NISP photometric system. A&A, 662:A92, June 2022. doi: 10.1051/0004-6361/202142897
-
[8]
Gillard, W. et al. Euclid Near Infrared Spectrometer and Photometer instrument in space. pages 13092–23, June 2024
work page 2024
Show all 20 references
-
[9]
A New Signal Estimator from the NIR Detectors of the Euclid Mission
Bogna Kubik et al. A New Signal Estimator from the NIR Detectors of the Euclid Mission. Publ. Astron. Soc. Pac., 128(968):104504, 2016. doi: 10.1088/1538-3873/128/968/104504
2016 doi
-
[10]
Long, Sylvia M
Knox S. Long, Sylvia M. Baggett, John W. MacKenty, and Adam G. Riess. Characterizing persistence in the IR detector within the Wide Field Camera 3 instrument on the Hubble Space Telescope. In Mark C. Clampin, Giovanni G. Fazio, Howard A. MacEwen, and Jacobus M. Oschmann Jr., e...
2012 doi
-
[11]
Long, Sylvia M
Knox S. Long, Sylvia M. Baggett, and John W. MacKenty. Characterizing Persistence in the WFC3 IR Channel: Finite Trapping Times. WFC3 Instrument Science Report 2013-06, 10 pages, July 2013
2013
-
[12]
Long, Sylvia M
Knox S. Long, Sylvia M. Baggett, and John W. MacKenty. Persistence in the WFC3 IR Detector: an Improved Model Incorporating the Effects of Exposure Time. WFC3 Instrument Science Report 2015-15, 18 pages, September 2015
2015
-
[13]
Cheng, Stephanie A
Gregory Mosby, Bernard Rauscher, Chris Bennett, Edward S. Cheng, Stephanie A. Cheung, Analia N. Cillis, David A. Content, David A. Cottingham, Roger D. Foltz, John D. Gygax, Robert J. Hill, Jeffrey W. Kruk, Jon S. Mah, Lane A. Meier, Chris A. Merchant, Laddawan R. Miko, Eric C...
2020
-
[14]
Characterization of H2RG IR detectors for the Euclid NISP instrument
Aur´ elia Secroun, Benoit Serra, Jean Claude Cl´ emens, Romain Legras, Philippe Lagier, Mathieu Niclas, Laurence Caillat, William Gillard, Andr´ e Tilquin, Anne Ealet, R´ emi Barbier, Sylvain Ferriol, Bogna Kubik, G´ erard Smadja, Eric Prieto, Thierry Maciaszek, and Anton Noru...
2016
-
[15]
Serra, A
B. Serra, A. Secroun, J. C. Cl´ emens, P. Lagier, M. Niclas, L. Caillat, J. Rodriguez-Ferreira, W. Gillard, A. Tilquin, A. Ealet, R. Barbier, B. Kubik, G. Smadja, S. Ferriol, E. Prieto, T. Maciaszek, and A. Norup Sorensen. Characterization of Euclid-like H2RG IR detectors for ...
2015
-
[16]
Serra, A
B. Serra, A. Secroun, J-C. Cl´ emens, P. Lagier, M. Niclas, L. Caillat, J. Rodriguez-Ferreira, W. Gillard, A. Tilquin, A. Ealet, R. Barbier, B. Kubik, G. Smadja, S. Ferriol, E. Prieto, T. Maciaszek, and A. Norup Sorensen. Characterization of Euclid-like H2RG IR detectors for t...
2015
-
[17]
Smith, Maximilian Zavodny, Gustavo Rahmer, and Marco Bonati
Roger M. Smith, Maximilian Zavodny, Gustavo Rahmer, and Marco Bonati. A theory for image persis- tence in HgCdTe photodiodes. In David A. Dorn and Andrew D. Holland, editors, High Energy, Optical, and Infrared Detectors for Astronomy III, volume 7021, page 70210J. Internationa...
2008 doi
-
[18]
Smith, Maximilian Zavodny, Gustavo Rahmer, and Marco Bonati
Roger M. Smith, Maximilian Zavodny, Gustavo Rahmer, and Marco Bonati. Calibration of image persistence in HgCdTe photodiodes. In David A. Dorn and Andrew D. Holland, editors, High Energy, Optical, and Infrared Detectors for Astronomy III, volume 7021, page 70210K. Internationa...
2008 doi
-
[19]
Predictive model of persistence in H2RG detectors
Simon Tulloch, Elizabeth George, and ESO Detector Systems Group. Predictive model of persistence in H2RG detectors. Journal of Astronomical Telescopes, Instruments, and Systems, 5(3):036004, 2019. doi: 10.1117/1.JATIS.5.3.036004. URL https://doi.org/10.1117/1.JATIS.5.3.036004
2019 doi
-
[20]
Waczynski, R
A. Waczynski, R. Barbier, S. Cagiano, J. Chen, S. Cheung, H. Cho, A. Cillis, J. C. Cl´ emens, O. Dawson, G. Delo, M. Farris, A. Feizi, R. Foltz, M. Hickey, W. Holmes, T. Hwang, U. Israelsson, M. Jhabvala, D. Kahle, Em. Kan, Er. Kan, M. Loose, G. Lotkin, L. Miko, L. Nguyen, E. ...
2016
Reviewed August 7, 2026 · model on record in the stance chip above.
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